Millions of mobile devices, such as mobile phones, are sold each year. As the mobile user base expands, so do device storage capacities and wireless services. Not only are these devices accumulating more device-resident data such as email, appointments and photos, but they are also increasingly used as front-end interfaces to ever-larger external data sets, including web sites, traffic information, and yellow pages data. Unprecedented volumes of data can be found in the pockets of users. At least a dozen simple message service (SMS) query-answer systems and web browser interfaces that target mobile platforms have debuted recently, and more are currently being developed.
As mobile devices continue to store and connect to these increasing volumes of data, the challenge becomes how to support users in finding information on devices with limited input and output capabilities. Small screens constrain the information that can be provided both during navigation and in the displayed results. Existing solutions cater to small screens and low bandwidth, but are modeled after desktop web search, posing three primary usability issues for the mobile setting. First, they rely on text entry as the method of input, even though the persistent trend toward smaller phones is directly at odds with the goal of achieving efficient text entry. Second, they focus on searching off the device, under-utilizing the device's processing power and storage capabilities. Finally, both the SMS and web search models support directed search tasks, but are less appropriate for browsing and exploratory search scenarios (“sense-making”) that are quite complementary to the mobile setting (e.g., “What is fun to do and inexpensive around here?”).